1. Field of the Invention
This invention relates to a polymer blend composition. More particularly, this invention relates to a polymer blend composition comprising a selectively hydrogenated block copolymer, a vinyl aromatic copolymer and a thermoplastic polyester.
2. Description of the Prior Art
Vinyl aromatic resins, such as polystyrene or high impact polystyrene have been found to be useful in thermoplastic molding compositions. However, such vinyl aromatic resins have poor heat distortion and impact resistance. One approach to improve these property deficiencies involves copolymerizing the vinyl aromatic with an .alpha., .beta.-unsaturated cyclic anhydride, to form copolymers such as poly(styrene-maleic anhydride). Although such copolymers have improved heat resistance, the overall balance of properties is still inadequate.
In order to further improve the properties of such vinyl aromatic copolymers, various other polymers have been blended with the copolymer. For example, blends of nitrile rubber and styrene-maleic anhydride copolymers are disclosed in U.S. Pat. Nos. 2,914,505 and 3,641,212. Blends of styrene-maleic anhydride copolymers with radial styrene-diene block copolymers and an optional polyphenylene ether resin are disclosed in U.S. Pat. No. 4,097,550. Still further, blends of styrene-maleic anhydride copolymers, hydrogenated styrene-diene block copolymers and optional polyphenylene ether resins are disclosed in U.S. Pat. Nos. 4,124,654 and 4,243,766. Such polymer blend compositions are still not ideal. A new thermoplastic molding composition with an unexpectedly improved balance of properties has now been found.